Chip-level equalizers are suitable candidates for CDMA receivers, such as those used in wireless transmit/receive units (WTRUs) and base stations. A normalized least mean square (NLMS)-based CLE receiver offers superior performance for high data rate services such as high speed downlink packet access (HSDPA) over a Rake receiver. A typical NLMS receiver consists of an equalizer filter and an NLMS algorithm. The equalizer filter is typically a finite impulse response (FIR) filter.
The NLMS algorithm is used as the tap coefficients generator. It generates appropriate tap coefficients used by the equalizer filter and updates them appropriately and iteratively in a timely basis. Typically, tap coefficients generation includes the error signal computation, vector norm calculation and leaky integration to generate and update the tap coefficients.
The high complexity of the CLE is due to the over-sampling processing in the CLE. A typical CLE includes equalizer filtering, tap-weight vector updating, vector norm square computing, or the like, which all operate at two or more times the chip rate. Two times the chip rate over-sampling processing induces twice as much complexity as the chip rate non-over-sampling processing in the equalizer filter.